2 stroke exhaust modifications

[hemi43]

I'm in the process of putting a Polaris 600 liberty engine in a Honda Odyssey for a friend, because the original engine crapped out.(I hate 2 strokes BTW)
What part of the expansion chamber can I mess around with without causing major engine issues ?
There's no way I can fit the stock pipe and manifold, without cutting it up a bit !!
I need to relocate the first 10 inches of the pipe in order to get it to fit the tight quarters.
Dan

[fabr]

The expansion chamber is the heart of a 2 stroke exhaust. Anything you do to it will change the power output,negatively or positively is the question.

[Spec]

Got some pix?
Welcome to my world
You really can't mess with the chamber without changing the pulse pattern, You can twist and turn it...But you need to keep the overall length,and reflection and reversion cones intact, and keep the pulse length intact as well,
Any changes in the 2 will affect scavenging or the cylinders Lean one out...And the motor will fry, get one with too much back pressure the motor will be doggy and self destruct, these are extreme conditions...but a real scenario
Your best bet,IMO...Get the volume, figured out...Get the the R cones angles...Know the distance from the port to the refraction cone...Those have to remain constant...Unless you are willing to retune the motor...
I've never PIPED a Liberty ...But The longer, thinner pipe will contribute to more torque and driveability in the woods...A shorter Fatter pipe will give an explosive acceleration at a given rpm

[LiveWire]

Is that a piston port triple? If so, I would highly suggest not using that engine.

[hemi43]

OK ! Here's some pics;

The picture below is the engine installed, and it cannot be moved. It's a 2004 Polaris Liberty liquid cooled twin.



These are the 2 pipes that I have to work with. The one on the right is the proper pipe for that engine. The one on the left is from a Rotax 670. as you can see, the inlet on the proper pipe is way further to the right than the 670's pipe.





Here's the proper pipe laying close to where it must end up. I want to reduce the radius so that it will be more inline with the exhaust manifold. The proper length will be retained, but the exhaust will have to turn more sharply.

I realize that this is not the best thing to do, but it must be done. If some power is lost doing this, we're OK with that, because this has more power than we will ever need. Another thing that must be modified is the manifold. It's difficult to see in the picture, but the outlet is too high, and must turn downwards about 45 degrees.









Here's a pic of the 670's pipe laying in place. This would be easier to use because the inlet turn so much more rapidly, but I'm reluctant to use it because it was not designed for this engine.

[fabr]

The one that dies LIVES with the most tools, wins !!



Just couldn't resist modifying your sig line quote.

[Odyknuck]

These pipes are more forgiving then we think. For example when we re shaped the pipe on my buddies 700 Rotax for his Pilot, we twisted it and made part of the expansion chamber longer. We also against my better judgement pie cut the two into one manifold (very similar to the one on your motor) to face down to get the required clearence behind the seat. The Motor runs like a raped ape. If he lost HP he does not notice it. When your dealing with a 100 plus HP you can afford to lose 10 or so on a 600# machine. Basically a few mods here and there is just not that critacal.

[hemi43]

Well, the pipe is in!!
I flipped the exhaust manifold, and cut 3 small pie sections out of the pipe. The pie sections were about 3/8 wide at the large end.
It fits perfect now!! I cant see this minor mod causing any issues.
 We had always planned to stretch the frame, but wanted to wait until the exhaust was done so that we would know how much to stretch by.
Dan

[fabr]

You should see  no difference in perf with that mod. Nice job.

[hemi43]

You should see  no difference in perf with that mod. Nice job.

Except for the welds !! I was embarassed to post that picture 

With the pipe being paper thin, coated with oil inside and rust on the outside, it didn't weld the best. Looking forward to getting an inch of mud on it !!

[fabr]

Seen a lot of OEM stuff a LOT worse.

[Odyknuck]

I dought there will be any difference in power.  This is how I did mine:

[LiveWire]

There is a lot of carbon inside the pipe. That gets drawn into the weld and makes it brittle. It is best to burn out the carbon before welding on a used pipe.

[Odyknuck]

I used a flap wheel and glass beeder to get the carbon off.

[hemi43]

I dought there will be any difference in power.  This is how I did mine:

OK HOLD THE PRESSES !! Tell me about that air filter !!